Modern search radars with rotating antennas typically have a first threshold which is adaptive to the front end noise to yield a constant false alarm rate (CFAR) and having maximum detection sensitivity to an envelope detected received radar return signal. With this type of detector it is difficult to extract the target range and azimuth coordinates with the accuracy inherent in targets having a high signal-to-noise ratio.
In the radar arts there are several known techniques for determining the location of the center of a target whose radar return is received at a radar station. The simplest technique is to display the entire analog hit pattern on a plan position indicator (PPI) and depend upon the radar operator to estimate the center of the target. Since most radars use a transmitter pulse length shorter than the required range accuracy it is only necessary to beam split the displayed target in azimuth for good location estimation. Another technique is to use a wide transmitted pulse but use a wide bandwidth receiver to preserve the leading edge rise time of the return signal to provide range accuracy at the expense of sensitivity. Still another technique is the use of a low dynamic range receiver, such as Dicke Fix, that restricts the range stretching of the target returns. More sophisticated radars use a transmitted "search" waveform with crude range accuracy followed by a transmitted "track" waveform, possibly with pulse comparison, to obtain target coordinates on a single hit basis by differentiation and monopulse techniques. A still further technique involves the splitting of each range cell and comparing the resulting target coordinates in a computer to obtain the target azimuth centroid.